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Sand as media of Art. Physical simulation of granular materials for facilitating artist interaction. Nafees Ahmed. Motivation. Sand animation is a performance art technique in which an artist tells stories by creating animated images with sand.

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Sand as media of Art


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    1. Sand as media of Art Physical simulation of granular materials for facilitating artist interaction Nafees Ahmed

    2. Motivation • Sand animation is a performance art technique in which an artist tells stories by creating animated images with sand. • Artists like IlanaYahav , KseniyaSimonova , Su Dabao , Joseph Valerio are bringing this amazing performance art media in front of the world and making it more and more famous everyday.

    3. Motivation • Introduction of multi touch user interfaces and screens is providing the opportunity of bringing this beautiful art media into the digital world. Example of multi-touch workspaces Microsoft Surface

    4. Challenges • Allowing the artist to use his both hand , fingers , palms in articulated way to produce almost infinitely many different ways of interacting with the virtual sand. • Simulating the sand granules in a visually accurate manner that can represent both the appearance and the physical interaction of real art-sand granules.

    5. Physics of Sand • What are the physical properties of sand? • What makes it different than other materials? • What mathematical equation can properly explain physical behavior of sand? • Sand falls into the more general category of granular materials.

    6. Physics of Sand “Granular solids, liquids, and gases”Heinrich M. Jaeger, Sidney R. Nagel , Robert P. BehringerReviews of Modern Physics, Vol. 68, No. 4, October 1996

    7. Physics of Sand • They are large conglomerations of discrete macroscopic particles. • If they are non-cohesive, then the forces between them are only repulsive so that the shape of the material is determined by external boundaries and gravity. • If the grains are dry, any interstitial fluid, such as air, can often be neglected in determining many, but not all, of the flow and static properties of the system.

    8. Yet despite this seeming simplicity, a granular material behaves differently from any of the other familiar forms of matter—solids, liquids, or gases—and should therefore be considered an additional state of matter in its own right.

    9. A sand pile at rest with a slope lower than the angle of repose behaves like a solid.

    10. At rest state, the pressure at the bottom of sand column is constant given enough depth. • This allows the construction of hour glass with sand rather than liquids.

    11. If the pile is titled beyond a specific angle, the granules start to flow, but unlike liquid the flow is confined within the boundary particles only.

    12. Even though flow in granular material feels like flowing liquid, it cannot be modeled using Navier-Stokes equation. • Due to lack of cohesive force, we might be tempted to model it as a dense gas, but in contrast to ordinary gas the energy is insignificant at the room temperature.

    13. Granular Material Simulations Steps common to all approaches, • Identify an application paradigm. • Select a subset of sand behavior relevant to the application. • Find the mathematical model that best describes the physical behavior. • Find a optimal implementation of the model. • Provide a way of rendering the sand model.

    14. Granular Material Simulations • X. Li and J. M. Moshell. “Modeling soil: Realtime dynamic models for soil slippage and manipulation.” proceedings of SIGGRAPH ’93, pages 361–368, 1993. • B. Chanclou, A. Luciani, and A. Habibi. “Physical models of loose soils dynamically marked by a moving object. ” Computer Animation, pages 27–35, 1996. • R. W. Sumner, J. F. O’Brien, and J. K. Hodgins. “Animating sand, mud, and snow.” Computer Graphic Forum, 18:3–15, Mar. 1999. • Y.L Zeng , C. I. Tan et al “A Momentum Based Deformation System for Granular Material” Computer Animation and Virtual Worlds - CASA 2007 Volume 18 Issue 4-5, September 2007 • Miller, G. and Pearce, A. “Globular dynamics: A connected particle system for animating viscous fluids.” Computers and Graphics, 13(3):305–309, 1989. • N. Bell, Y. Yu, and P. J. Mucha. “Particle-based simulation of granular material.” ACM SIGGRAPH/Eurographics Symposium on Computer Animation, 2005. • Zhu, Y. and Bridson, R. “Animating sand as a fluid.” ACM SIGGRAPH 2005 Papers, pages 965–972. ACM Press, New York, NY, USA, 2005. • Monaghan, J. J. “Smoothed Particle Hydrodynamics. “ Annual review of astronomy and astrophysics, 30(A93-25826 09-90):543–574, 1992. • Lenaerts, T. and Dutr´e, P. “Mixing fluids and granular materials.” Computer Graphics Forum, 28(2):213–218, 2009b. • Aldu´an, I., Tena, ´A., and Otaduy, M. A. “Simulation of high-resolution granular media.” In Proc. of CongresoEspa˜nol de Inform´aticaGr´afica. 2009. • K. Onoue and T. Nishita. “An interactive deformation system for granular material.” Computer Graphics Forum, 24(1):51–60, Mar. 2005. • K. Onoue and T. Nishita. “Virtual sandbox.” Proceedings of the 11th Pacific Conference on Computer Graphics and Applications, pages 252–259, 2003. • Rungjiratananon, W., Szego, Z., Kanamori, Y., and Nishita, T. “Real-time animation of sand-water interaction”. In Computer Graphics Forum (Pacific Graphics 2008), volume 27, pages 1887–1893. 2008. • Pla-Castells, M., Garc´ıa-Fernandez, I., and Martinez-Dura, R. J. “Physically based interactive sand simulation.” In Mania, K. and Reinhard, E., editors, Eurographics 2008 - Short Papers, pages 21–24. 2008.

    15. Height Field Particle Based Continuum MP89 1990 M92 LM93 CLH96 SBH99 2000 ON03 ZB05 BYM05 ZT07 PGM08 ATO09 RSKN08 LD09 2010

    16. Height Field Particle Based Continuum MP89 1990 M92 LM93 CLH96 SBH99 2000 ON03 ZB05 BYM05 ZT07 PGM08 ATO09 RSKN08 LD09 2010 “Modeling soil: Realtime dynamic models for soil slippage and manipulation.”X. Li and J. M. Moshell. proceedings of SIGGRAPH ’93, pages 361–368, 1993.

    17. Height Field Particle Based Continuum MP89 1990 M92 LM93 CLH96 SBH99 2000 ON03 ZB05 BYM05 ZT07 PGM08 ATO09 RSKN08 LD09 2010 “Physical models of loose soils dynamically marked by a moving object. ” B. Chanclou, A. Luciani, and A. Habibi.Computer Animation, pages 27–35, 1996.

    18. Height Field Particle Based Continuum MP89 1990 M92 LM93 CLH96 SBH99 2000 ON03 ZB05 BYM05 ZT07 PGM08 ATO09 RSKN08 LD09 2010 “Animating sand, mud, and snow.” R. W. Sumner, J. F. O’Brien, and J. K. Hodgins.Computer Graphic Forum, 18:3–15, Mar. 1999.

    19. Height Field Particle Based Continuum MP89 1990 M92 LM93 CLH96 SBH99 2000 ON03 ZB05 BYM05 ZT07 PGM08 ATO09 RSKN08 LD09 2010 “Virtual sandbox.” K. Onoue and T. Nishita.Proceedings of the 11th Pacific Conference on Computer Graphics and Applications, pages 252–259, 2003.

    20. Height Field Particle Based Continuum MP89 1990 M92 LM93 CLH96 SBH99 2000 ON03 ZB05 BYM05 ZT07 PGM08 ATO09 RSKN08 LD09 2010 “A Momentum Based Deformation System for Granular Material” Y.L Zeng , C. I. Tan et alComputer Animation and Virtual Worlds - CASA 2007 Volume 18 Issue 4-5, September 2007 .

    21. Height Field Particle Based Continuum MP89 1990 M92 LM93 CLH96 SBH99 2000 ON03 ZB05 BYM05 ZT07 PGM08 ATO09 RSKN08 LD09 2010 “Globular dynamics: A connected particle system for animating viscous fluids.” Miller, G. and Pearce, A.Computers and Graphics, 13(3):305–309, 1989.

    22. Height Field Particle Based Continuum MP89 1990 M92 LM93 CLH96 SBH99 2000 ON03 ZB05 BYM05 ZT07 PGM08 ATO09 RSKN08 LD09 2010 “Particle-based simulation of granular material.” N. Bell, Y. Yu, and P. J. Mucha. ACM SIGGRAPH/Eurographics Symposium on Computer Animation, 2005.

    23. Height Field Particle Based Continuum MP89 1990 M92 LM93 CLH96 SBH99 2000 ON03 ZB05 BYM05 ZT07 PGM08 ATO09 RSKN08 LD09 2010 “Real-time animation of sand-water interaction”. Rungjiratananon, W., Szego, Z., Kanamori, Y., and Nishita, T.In Computer Graphics Forum (Pacific Graphics 2008), volume 27, pages 1887–1893. 2008.

    24. Height Field Particle Based Continuum MP89 1990 M92 LM93 CLH96 SBH99 2000 ON03 ZB05 BYM05 ZT07 PGM08 ATO09 RSKN08 LD09 2010 “Smoothed Particle Hydrodynamics. “ Monaghan, J. J. Annual review of astronomy and astrophysics, 30(A93-25826 09-90):543–574, 1992

    25. Height Field Particle Based Continuum MP89 1990 M92 LM93 CLH96 SBH99 2000 ON03 ZB05 BYM05 ZT07 PGM08 ATO09 RSKN08 LD09 2010 “Animating sand as a fluid” Zhu, Y. and Bridson, R..” ACM SIGGRAPH 2005 Papers, pages 965–972. ACM Press, New York, NY, USA, 2005.

    26. Height Field Particle Based Continuum MP89 1990 M92 LM93 CLH96 SBH99 2000 ON03 ZB05 BYM05 ZT07 PGM08 ATO09 RSKN08 LD09 2010 “Mixing fluids and granular materials.” Lenaerts, T. and Dutr´e, P.Computer Graphics Forum, 28(2):213–218, 2009b.

    27. Height Field Particle Based Continuum MP89 1990 M92 LM93 CLH96 SBH99 2000 ON03 ZB05 BYM05 ZT07 PGM08 ATO09 RSKN08 LD09 2010 “Simulation of high-resolution granular media.” Aldu´an, I., Tena, ´A., and Otaduy, M. A.In Proc. of CongresoEspa˜nol de Inform´aticaGr´afica. 2009.

    28. Height Field Approach

    29. [LM93] [CLH96]

    30. “Animating sand, mud, and snow.” R. W. Sumner, J. F. O’Brien, and J. K. Hodgins.Computer Graphic Forum, 18:3–15, Mar. 1999.

    31. Collision with rigid object. • For each column, a ray is cast from the bottom of the column through the vertex at the top. • If ray intersects rigid surface before the field height then there is a collision. • Computation cost in collision is reduced by partitioning the polygons of rigid body models using an axis aligned bounding box hierarchy.

    32. Displacement • Using vertex coloring algorithm, simulation computes a contour map with the distance from each column that has collided with the object to the closest column that has not collided. And also the depth of displacement.

    33. Ground materials from the columns that are in contact is either compressed or distributed. • The compression ratio is defined as . Hence the material to be distributed is • The uncompressed material is equally distributed to the nearest column with no contact. • The heights of columns in the ring around the contour is increased to reflect this transfer.

    34. Erosion • Erosion algorithm identifies columns with steep slope and moves materials between them to stabilize the height field. • For a column and a neighboring column the slope is, • If slope is greater than then material is moved. • Material is moved by computing average difference of n neighboring columns,

    35. The average difference is multiplied by a fractional constant . • The algorithm runs until all slopes are below a threshold • In special case when neighbor column is in contact with geometric object the angle is • The use a particle system to model the “splash” when rigid object is thrown into the sand.

    36. “A Momentum Based Deformation System for Granular Material” Y.L Zeng , C. I. Tan et alComputer Animation and Virtual Worlds - CASA 2007 Volume 18 Issue 4-5, September 2007 .

    37. This paper additionally provides impression of objects momentum in deforming the sand terrain. • While determining the displaced material, it takes into count the horizontal and vertical component of velocity. • The vertical component is equally distributed as the previous paper. • The horizontal component is favored to the direction of the velocity.

    38. “Virtual sandbox.” K. Onoue and T. Nishita.Proceedings of the 11th Pacific Conference on Computer Graphics and Applications, pages 252–259, 2003.

    39. Particle Based Approach • Consider sand granule as simulation unit. • Use newtonian laws of motion to compute interaction between granules • Reduce computation of real physical simulation with some simplifying assumptions • Use special boundary conditions to produce visually correct results

    40. “Globular dynamics: A connected particle system for animating viscous fluids.” Miller, G. and Pearce, A.Computers and Graphics, 13(3):305–309, 1989.

    41. A generic simulation model for any natural object that can be represented as connected set of “blobs” , like lava, mud , slime , oil , salad dressing , meltable solids, sand etc. • They refer to the unit element of the connected particle system as a “Globule”, which literally means “sphere like” • The system is built upon parameterized “soft” collision between globules . The parameters and the final rendering method of the globules define what kind of simulation is being done.

    42. Globule to globule forces • The positional change in the globule over the time step (t) is calculated by double integration of sum of forces acting on the particle: